Driving mechanism for components of optical objective



March 22, 1966 K. BROLDE 3,241,470

DRIVING MECHANISM FOR COMPONENTS OF OPTICAL OBJECTIVE Filed March 10, 1964 1/2 vemor:

KURT BROLDE United States Patent 9 3,241,470 DRIVING NHEQHANISM FOR COMPONENTS OF OPTICAL OBJECTIVE Kurt Brolde, Bad Kreuznach, Germany, assignor to Jos.

Scheider & 00., Bad Kreuznach, Germany, a corporation of Germany Filed Mar. 10, 1964, Ser. No. 350,709 Claims priority, application Germany, Mar. 16, 1963, Sch 32,949 2 Claims. (Cl. 95-45) My present invention relates to a driving mechanism for the controlled displacement of a load, more particularly of one or more movable components in a photographic or cinematographic camera objective with substantially constant but adjustable driving speed. The invention is specifically directed to a varifocal objective with axially displaceable optical components which, for the purpose of providing a so-called zoom effect, are to be moved automatically within predetermined limits to increase or reduce the effective focal length and image scale of the objective.

In commonly assigned application Ser. No. 132,029, filed August 17, 1961, by Paul Himmelsbach, now Patent No. 3,165,044, there has been disclosed a system of this general type including an electric motor connected in series with an adjustable resistor. Such a system, though useful for most purposes, does not satisfy the most stringent requirements of accuracy in situations in which an absolutely smooth adjustment is important, as may be the case in professional motion-picture production. Thus, with the usual type of drive motor (e.g., shunt-type DC. motor) adapted to be used with portable sources of current, e.g., conventional flashlight batteries, small changes in the torque needed to overcome the mechanical resistance of the load may alter the internal resistance of the motor to a considerable degree-in relation to the seriesconnected control resistor-so that the available driving voltage and therefore the motor speed tend to vary. Such changes in torque, however, occur to a greater or less extent wherever the drive of the adjustable components includes a system of cams, as in the case of varifocal objective, designed to convert a constant-speed drive into an adjustment motion which follows a nonlinear law. The alternative of using an adjustable resistor in shunt with the motor circuit is even less satisfactory because of the large current drain which cannot be tolerated in a system using portable batteries.

The general object of my invention, therefore, is to provide an improved driving mechanism of the character set forth which can be readily miniaturized, does not draw excess current and insures maintenance of a constant driving speed within a predetermined range of adjustability.

This object is realized, in accordance with my invention, by the provision of a transistor in the energizing circuit of an electric driving motor which also includes a switch for starting and stopping the motor, the transistor having a pair of output electrodes (e.g., emitter and collector) in series with the motor and its power source and further having a control electrode (e.g., base) connected to a point of adjustable potential on a variable-resistance device which is bridged across the power source in series with the switch. By this means, the motor and the variable-resistance device are fully de-energized in the open state of the switch whereas only a minimum of biasing current, just sufficient to control the conductivity of the transistor, is drawn by the variable-resistance device when the motor is in operation. This device may simply be an adjustable resistor or potentiometer, though of course some more elaborate adjustable impedance means (e.g., another transistor stage) could be used in its place.

3,241,470 Patented Mar. 22, 1966 In the case of a camera objective for which the system according to the invention is primarily intended, be it for the adjustment of focal length or some other parameter (e.g., range or diaphragm aperture) thereof, the switch will generally be of the polarity-reversing type so that the motor may be driven at the selected speed in either of two directions. In such case, if the load and its motor are displaced manually by the user in the open-circuit condition of the automatic drive, the residual magnetism of the motor field could give rise to circulating currents, however small, which in turn would tend to impede the manual adjustment of the parts. To inhibit the circulation of such residual currents, I prefer to include in the motor circuit suitably poled diodes which will also help to suppress current surges on starting and stopping. The biasing circuit, in turn, may be protected against undesirable voltage fluctuations by a further diode or diodes.

The invention will be described in greater detail hereinafter, reference being made to the accompanying drawing in which:

FIG. 1 is a combination of a side-elevational view (parts broken away) of a varifocal camera objective with a diagrammatic illustration of the energizing circuit of an associated drive motor; and

FIG. 2 is a rear view of the objective shown in FIG. 1.

In FIGS. 1 and 2 I have shown at 1 the housing of a conventional varifocal objective attached by a threaded boss 1a to the body of a camera 2 which has been indicated only schematically in dot-dash lines. The optical components of objective 1 include a pair of lenses 3 (dispersive) and 3a (collective) which are jointly displaceable along the optical axis of the objective, upon rotation of a cammingsleeve 5 having slots 4 and 4a in which studs 3' and 3" of lenses 3 and 3a respectively engage. Sleeve 5 is rigid with a ring gear 6 which meshes with a pinion 7 driven, in its turn, by a pinion 8 which derives its rotaton from a motor 9 through the intermediary of a reduction gearing 9a. The motor 9, its speed reducer 9a and the associated pinions 7, 8 are disposed inside a casing 10, attached to the bottom of objective housing 1, which in the illustrated embodiment also contains one or more dry cells 11 constituting the source of power for the motor. Naturally, the source of power could also be located inside the camera 2 or in a separate attachment.

As diagrammatically indicated in FIG. 1, the energizing circuit for motor 9 includes, in addition to power source 11, a transistor 12 having its collector electrode connected to the negative terminal of battery 11 and having its emitter electrode tied to one contact arm a of a double-pole, double-throw switch 15. The positive terminal of battery 11 is connected to the second contact arm b of that switch. The two stationary contact pairs associated with the arms a and b are tied by way of respective leads 18, 19 to the input terminals of motor 9 which may be a shunt-type or permanent-magnet-type D.-C. motor. A biasing potentiometer 13, having its variable tap connected to the base electrode of transistor 12, extends between the negative terminal of battery 11 and the junction 20 of conductors 18 and 19; these conductors contain respective diodes 16 and 17 which are oppositely poled, with reference to the closed circuit 18, 19 still existing in the open position of switch 15, to prevent the circulation of currents induced in the armature of motor 9 upon'any rotation of sleeve 5 by manual control means not further illustrated. Another diode 14 serves to maintain the voltage drop across resistor 13 substantially v switch arm b, lead 18, armature (and possibly field) windings of motor 9, lead 19 and the collector-emitter circuit of transistor 12 back to the negative terminal of source 11, another current path leading from conductor 19 via diode 17 and the biasing circuit 13, 14 to the same negative terminal. As the conductivity of transistor 12 is determined by the setting of the tap of potentiometer 13, a constant current will flow in the main circuit through motor 9. This circuit also includes a pair of limit switches 21, 22 of which only the former is effective in the position of switch 15 assumed above, switch 21 being opened in any convenient way (e.g., by an abutment on sleeve 5 as disclosed in the Himmelsbach application referred to above) as soon as the movable system 3, 3a reaches the end of its stroke. Conversely, if switch 15 were thrown into its opposite position, motor 9 would be energized in the reverse direction by way of closed' limit switch 22 and the biasing current for resistor 13 would pass through diode 17 rather than 16, there being no other change in the operation of the circuit.

My invention is, of course, not limited to the specific arrangement described and illustrated, nor to the particular use herein disclosed, but may be modified in various ways and adapted to analogous uses in a manner which will be readily apparent to persons skilled in the art; such modifications and adaptations are, therefore, intended to be embraced within the spirit and scope of the appended claims.

I claim:

1. A driving mechanism for the controlled displacement of a load at adjustable speed, comprising an electric motor, an energizing circuit for said motor including a source of current and switch means in series with said source, variable-resistance means connected across said source in series with said switch means, and a transistor 35 with a pair of output electrodes connected between said source and said switch means to define a variable control resistance in series with said switch means and said source, said transistor being further provided with a control electrode tied to a point of adjustable potential on said variable-resistance means for varying the magnitude of said control resistance, said transistor being thus fully de-energized in the open state of said switch means.

2. A driving mechanism for the controlled displacement of a load at adjustable speed, comprising an electric motor, an energizing circuit for said motor including a source of direct current and polarity-reversing switch means in series with said source, variable-resistance means connected across said source in series with said switch means, a transistor with the pair of output electrodes connected between said source and said switch means to define a variable control resistance in series with said switch means and said source, said transistor being further provided with a control electrode tied to a point of adjustable potential on said variable-resistance means, said transistor being thus fully de-energized in the open state of said switch means, and diode means for varying the magnitude of said control resistance in series with said motor for inhibiting the circulation of residual currents in said circuit upon the opening of said switch means.

References Cited by the Examiner UNITED STATES PATENTS JOHN M. HORAN, Primary Examiner. 

1. A DRIVING MECHANISM FOR THE CONTROLLED DISPLACEMENT OF A LOAD AT ADJUSTABLE SPEED, COMPRISING AN ELECTRIC MOTOR, AN ENERGIZING CIRCUIT FOR SAID MOTOR INCLUDING A SOURCE OF CURRENT AND SWITCH MEANS IN SERIES WITH SAID SOURCE, VARIABLE-RESISTANCE MEANS CONNECTED ACROSS SAID SOURCE IN SERIES WITH SAID SWITCH MEANS, AND A TRANSISTOR WITH A PAIR OF OUTPUT ELECTRODES CONNECTED BETWEEN SAID SOURCE AND SAID SWITCH MEANS TO DEFINE A VARIABLE CONTROL RESISTANCE IN SERIES WITH SAID SWITCH MEANS AND SAID SOURCE, SAID TRANSISTOR BEING FURTHER PROVIDED WITH A CONTROL 